Meanwhile, the number of Inc. 500 businesses that publish a corporate blog has fallen over the past year, the study found, as companies appear to be shifting away from maturing tools (e.g., blogs, message/bulletin boards, online video, and podcasting) toward popular platforms such as Facebook, Twitter, LinkedIn, YouTube, and Foursquare.

Key social media-related findings among companies listed on the 2011 Inc. 500, according to the study:

Facebook and Twitter use is still growing, albeit slightly: 73% of Inc. 500 companies use Facebook, up from the 71% that did so in 2010, and 64% use Twitter, up from 59%.

Blogging and online video are down: 37% of Inc. 500 companies now publish a blog, down from 50% in 2010, and 24% use online video (vs. 33% in 2010). Among those not using blogging, 56% plan to start, whereas only 34% of those not using online video plan to do so.

Across other social channels and digital marketing activities, LinkedIn enjoys nearly the same popularity as Facebook among the Inc. 500:

73% use LinkedIn and 45% use YouTube (adoption levels were not measured in 2010).

13% use Foursquare, up from 5% in 2010.

Some 14% of Inc. 500 companies are developing mobile applications (that activity was not measured in 2010).

Blogging: Inc. 500 vs. Fortune 500

Among the Inc. 500, the use of blogging may have peaked as a primary social media tool. By contrast, among Fortune 500 companies, blogging has leveled off over the past three years, at roughly 23% penetration:

Facebook, LinkedIn Most Effective Overall

Asked to define the single most effective social networking platform they use, 25% of Inc. 500 companies cite Facebook, and 24% cite LinkedIn.